In oil and gas wells where formation sand is unconsolidated, there is migration of sand particles into the wellbore as fluid is produced. Such migration may cause production loss due to the sand bridging in the casing, the tubing or the flowbore; failure of the casing or the liners; compaction or erosion; abrasion of the downhole or the surface equipment; and handling and disposal of produced formation materials. Therefore, there is a need to prevent such sand migration by either chemical or mechanical means. One method of sand control which is used extensively is that of gravel packing. In general, gravel packing includes the installation of a screen adjacent the formation downhole followed by the packing of gravel in the perforations and around the screen to prevent the sand from migrating from the formation to the production tubing. In such an arrangement, a gravel screen assembly attached to a work string is lowered downhole through an open hole or a cased borehole and adjacent the formation to be completed. A slurry of gravel suspended in a viscous carrier fluid is pumped downhole through the work string and a cross-over assembly into the annulus. Pump pressure is applied to the slurry forcing the suspended gravel through the perforations or up against the formation sand. The gravel then accumulates in the annulus between the screen and the casing or the formation sand. The gravel forms a barrier which allows the flow of hydrocarbons therethrough but inhibits the flow of sand particles into the production tubing which would sand up the well.
There are various methods used in gravel packing operations, the most advantageous being the crossover method. The crossover method, in general, utilizes a standard gravel pack assembly including a gravel screen and a washpipe therewithin. It also utilizes a packer and a crossover assembly at the top of the gravel pack assembly. The packer is set mechanically by rotation of the work string. The packer is located above the crossover assembly and forms a lower borehole annulus adjacent the formation and an upper borehole annulus above the formation. The crossover assembly allows the slurry flowing down the flowbore of the work string above the screen assembly to cross over into the lower borehole annulus below the packer and around the gravel screen adjacent the formation. The gravel is deposited in the formation and lower borehole annulus with the fluid carrier continuing up the washpipe and flowing back through the crossover assembly to the upper annulus above the packer and up to the surface. The advantages of the crossover method are that, by pumping the slurry down the flowbore of the work string, no debris can be scoured from the casing by the slurry and deposited in the perforations to block the perforations to flow; the upper zone perforations or bond casing are subjected to less pressure; the gravel placement time and the chances of sand bridging are reduced; and the fluid and the gravel location are controlled within the work string.
Following the gravel packing operation, it is intended that the work string including a packer and a washpipe assembly be lifted to the surface leaving the gravel pack screen assembly at the bottom of the well. Therefore, a release mechanism is necessary to detach the gravel pack screen assembly from the work string. It is a principal objective that the two are separated without disturbing the completed gravel pack and that the separation does not fail because such failure will cause the destruction of the gravel pack.
Release mechanisms for releasing tools from tool strings downhole in general and, more particularly, for releasing gravel packing assemblies are well known. See for example the releasing assemblies in the gravel pack hardware manufactured by Baker Sand Control, Brown Oil Tools, Dowell and Texas Iron Works disclosed in the 1982-83 Composite Catalog of Oil Field Equipment and Services at page 991-992, 1459, 2522 and 7947 respectively. Another releasing tool used in gravel packing operations is disclosed in U.S. Pat. No. 4,175,778. Release tools for releasing tools downhole are disclosed in U.S. Pat. Nos. 2,409,811, 4,187,906, 4,190,107 and 4,289,202.
Most prior art release mechanisms of gravel packing assemblies are activated by rotating the work string. Rotation of the work string is not desirable because it is difficult to implement in slanted and crooked wells; it causes operating problems because of all the auxiliary piping extending from the surface downhole; it requires rotating equipment to rotate the packer, the crossover assembly and the washpipe assembly free from screen and hook-up nipple assembly; and it is unreliable and may not release. Release mechanisms which operate by rotation are shown in the sand control equipment on pages 991-992, 1459, 2522 and 7947 in the aforementioned Composite Catalog of Oil Field Equipment.
Prior art release tools that are not activated by rotation are disclosed in U.S. Pat. Nos. 2,409,811 and 4,175,778. The release tool disclosed in U.S. Pat. No. 2,409,811 is not specifically related to gravel packing operations, but to downhole releasing tools in general. It includes a plurality of balls partly positioned within holes in the retaining member and within apertures in the retained member, thereby locking both members together. The balls are kept in that locking position by a piston which is in intimate contact with the retaining member. If the piston is displaced, the intimate contact is eliminated and the balls move away from the apertures of the retained member whereby the connection between the two members is unlocked and the retaining member may be removed from the retained member. The piston, which has an internal passageway in series with the flowbore of the work string, is displaced by applying hydraulic pressure on it through the flowbore of the work string after the passageway is closed by a steel ball. The hydraulic pressure is not relieved by the displacement of the piston alone, but by the relative displacement of the retaining and retained members.
The tool disclosed in U.S. Pat. No. 4,175,778 is used to release gravel packing screens and discloses a plurality of blocks with chamfered surfaces partly positioned within holes in the retaining member and partly positioned within an annular groove in the hook-up nipple of the gravel packing screen thereby locking the two together. The blocks are held in that position by the interior surface of the piston which is in intimate contact with the interior of the retaining member adjacent the apertures. In order to release the hook-up nipple and the gravel packing assembly, the piston, which has an internal passageway in series with the flowbore of the tubing string, is displaced by closing the passageway with a steel ball and applying hydraulic pressure on it from the flowbore of the work string. When the piston is displaced, the blocks are no longer held in the locked position and the hook-up nipple is released. The hydraulic pressure is relieved by the displacement of the piston which exposes a relief port to the annulus.
One disadvantage of the release tools, which do not use rotation and which are disclosed in U.S. Pat. Nos. 2,409,811 and 4,175,778, is that they are not integral with the crossover assembly. This is also a disadvantage of some of the rotational releasing tools such as one of the tools shown on page 991 of the aforementioned Catalog.
Another disadvantage of the prior art, is that the release assembly cannot be activated until after the gravel packing operation is completed. Therefore, it is often necessary to repeat the time consuming and costly gravel packing operation because the release mechanism fails and such failure is not detected until the gravel packing operation has been performed. For this reason, there is a need for a release device which can release the gravel pack assembly before gravel packing commences so that any failure may be detected before valuable time and money is expended. The prior art cited above discloses release tools which release the gravel pack assembly after the operation is completed.
Some prior art release tools release the gravel pack screen together with the packer used in the operation and do not provide for the release of the gravel screen only. Therefore, an operator is often limited to using the packer for the gravel pack operation as the production packer. The Baker Sand Control, Brown Oil Tool, Dowell and Texas Iron Works Tools shown in the 1982-83 Composite Catalog of Oil Field Equipment and Services at pages 992, 1459, 2522 and 7947 are limiting in that respect.
The present invention overcomes the present deficiency of the prior art.